This invention relates to automatic stud driving tools used, for example, in the automotive and furniture industries and more particularly to automatic stud driving tools having a collarless retention mechanism for retaining the driven head of the stud driving tool. These stud driving tools are typically able to grasp a stud and thread it into a workpiece, and are then capable of automatically releasing the stud without the requirement that the stud be unthreaded from the tool.
Automatic stud drivers are known in which a stud is rotated to thread or screw the stud into a workpiece. For example, see U.S. Pat. Nos. 4,819,519; 4,590,826; 4,513,643; 4,476,749; 4,470,329; and 4,371,354. The above-referenced patents can be categorized into two groups regarding the structure retaining a driven head within a body. The first group, as typified by U.S. Pat. No. 4,513,643 and shown in FIG. 1 and assigned to the same assignee as the present invention (the disclosure of which is herein incorporated by reference), contains a cylindrical body member 10 provided with a uniform thread on an exterior surface thereof and an interior surface defining a cylindrical cavity for receiving a driven head 30. During assembly, the driven head 30 is positioned in the interior cavity of body 10 and a collar 20 is threadably attached over the driven head on the exterior thread of body 10 to retain driven head 30 within the cavity. Usually a lock ring 200 is threadably attached on the external threads of body 10 and the collar 20 mates with lock ring 200 to lock the collar in place. In order to ensure free rotation of the driven head 30 during loaded conditions, there is preferably about 0.010 inch free end play of the driven head 30. This can be accomplished by fixedly attaching the lock ring 200 in a predetermined location, such as by locktite. This free end play produces run-out, but if the free-play were reduced (by lowering the lock ring 200 and consequently permitting the collar 20 to move longitudinally closer to the body 10), the driven head may be locked-up. This type of assembly, although it allows for easy assembly, requires extra machining on the body as well as a separate collar and lock ring. This type of assembly does not provide an accurate repeat of collar position upon repeated tool assembly and disassembly since the collar may be tightened or loosened to various positions. Further, the assembly collar 20 can shift side to side as much as 0.005", so a looser fit than optimal must be used between the outer diameter of a top portion of the driven head 30 and an aperture on the collar 20 for sliding over the driven head.
The second group can be best described with reference to FIG. 2, which is the assembly of U.S. Pat. No. 4,371,354 assigned to the same assignee as the present invention (the disclosure of which is herein incorporated by reference). This assembly typically comprises a cylindrical base 10 and a cylindrical sleeve 12 rotatable relative to, but longitudinally secured within base 10. The sleeve 12 comprises a cavity which is internally threaded to house a compression spring 32, an adjuster 34 and a socket engaging head 14. The adjuster 34 can be readily rotated within the cavity to adjust the spring force and is fixedly held in place by removable set screws 36. The socket engaging head 14 is externally threaded to cooperate with the internally threaded sleeve 12 and is threadably rotated until mated with an upper surface of cylindrical sleeve 12.
The retention mechanisms for the driven head in these known automatic stud drivers are satisfactory for most stud driving applications. However, the need has arisen for an automatic stud driver having superior concentricity and reduced longitudinal axis play to reduce run-out, allowing use in highly automated applications with minimal supervision while providing quality stud driving precision. Additionally, there is a need for an automatic stud driver which can be more easily manufactured with less parts and which can be easily assembled or disassembled.